Diamond-Like Carbon (DLC)

Diamond-like Carbon is the name attributed to a variety of amorphous carbon materials containing a large fraction of sp³ bonds [1]. The sp³ fraction can vary from 0 to 90% and determines the density and the mechanical properties [2]. The sp² configuration and clustering determine the DLC optical properties [2]. Thus, a wide range of DLC films with different properties can be grown, depending on the source used and the deposition parameters [1]. The term tetrahedral amorphous carbon (ta-C) designates a non-hydrogenated carbon film containing a high fraction of sp³ bonded carbon. Thus, ta-C is the DLC with the highest density, Young's modulus and hardness [1, 2]. The introduction of hydrogen (H) or nitrogen (N) allows the deposition of hydrogenated amorphous carbon (a-C:H) and carbon nitride (CNx) films.

In recent years, there have been important advances in the science of carbon such as the development of chemical vapor deposition of diamond, the discovery of fullerenes, carbon nanotubes and graphene. However, DLC is the only nanostructured carbon-based material, which finds various applications in “real life” [2]. This is because of its unique set of properties, which include: high hardness, low friction, wear and chemical resistance to acids and alkalis, good thermal stability and ultra-smoothness [1, 2]. These films generally reproduce substrate topography, thus they do not need any post-finishing, which is required for diamond coatings. Thus, DLC is often used for tribological applications. DLC is also a biocompatible material and it can be used in the human body for medical purposes. Recently DLC has been used also for MEMS (Micro-Electro-Mechanical-Systems) and as gas-barrier coating for plastic bottles, containing sparkling liquids, in order to increase the bottle storage time [2]. At present, one of the most important industrial applications of the family of amorphous carbon coatings is in data storage devices, both magnetic and optical, where developments of DLC as a protective layer could allow increases of the data storage density up to ~1 Tbit/in² and ~60 Gbit/in², respectively [2].

1. J. Robertson. Mat. Sci. Eng. Rep., R37, 129 (2002)

2. C. Casiraghi, J. Robertson, A. C. Ferrari, Diamond-like carbon for data and beer storage, Materials Today vol 10 (2007)